Forum

It's useful to have the altitude data displayed, particularly the profile, but the accuracy from a GPS device is often not very good. This is particularly so when the device hasn't been 'locked on' for long, when among tall buildings, or below dense foliage.
When uploading GPS data, it would be useful to have the option for wikiloc to retrieve SRTM data (see http://en.wikipedia.org/wiki/Shuttle_Ra ... hy_Mission) and use that instead (as for example OziExplorer can do - see http://www.oziexplorer3.com/ozi3d/height_data.html). These data will usually be much more accurate and therefore of more benefit to those interested in the route.
Regards,
Rob

Hi Rob,

At Wikiloc we are currently using Asterdem (http://www.gdem.aster.ersdac.or.jp/) to calculate altitude for those tracks uploaded which don't have it. It is actually more accurate than SRTM as it provides an accuracy of only 30m globally, whereas SRTM "only" 30m in the USA and 90m everywhere else. So when you download a track which didn't have altitude in the beggining, the accuracy will be around 30m. This service comes with an associated cost, so no extra calculations are done for tracks which already have altitude added by the GPS itself.

Cheers,
Edu
Wikiloc

Thanks for the information, Edu.

As Wikiloc uses Asterdem, but only on those uploaded routes that have no altitude data, I was at first inclined to remove my GPS altitude data before uploading. However, you mention that there’s a cost to Wikiloc for obtaining the data and they have chosen not to change any elevation data that are already present.

Because of that, before uploading routes I may replace my GPS data with SRTM data (as it’s free) using third-party software. While accepting it won’t be as good as the Asterdem data, it’s likely to be somewhat better than my GPS data.

My original suggestion was to include an option (selected by the person uploading) for Wikiloc to replace GPS elevation data with data from an altitude database. (I suggested SRTM as I wasn’t aware of Asterdem.) I believe this will still be worth considering if/when Asterdem stop charging or Wikiloc are happy to use SRTM data as a free improvement on GPS data.

Kind regards,
Rob

Thanks for the suggestions. It could be an interesting option to let the user choose to replace altitude data for tracks uploaded. It's actually not viable if we get charged for the service but if Asterdem becomes free or we could change to another service (too much on our plate to switch right now) it's something definitely to have in mind.

Thanks again Rob!